Introduction - Geodesy: Introduction to Geodetic Datum and Geodetic Systems - page 12

1.3 Brief History and Trends in the Development
of Geodesy

1.3.1 Brief History of Geodesy

Geodesy has been gradually formed and developed as man's knowledge of the
Earth has increased (Vanicek and Krakiwsky 1986; Jiang 1992; Torge and M¨ ller
2012).

Embryonic Stage

Before the seventeenth century, geodesy was still in its embryonic state. In the third
century B.C., Eratosthenes from Alexandria first used the relationship between the
length S and the corresponding central angle

of arc AB of the circumference and
the circle's radius R in geometry to estimate the length of the Earth's radius (see
Fig. 1.1 ). Since the two endpoints A and B of arc AB are approximately on the same
meridian, the survey later developed into meridional arc measurement on this basis.
In 724 AD, under the guidance of Zhang Sui (monk Yixing), Nan Gongyue in China
Tang Dynasty first measured a meridian arc of about 300 km in the present Henan
Province. Other countries also did similar work one after another. However, due to
the rough techniques and the primitive measuring tools, although presumably the
most precise tools available in former times, the accuracy yielded was rather low.
This can only be seen as man's initial attempt to measure the size of the Earth.

γ

Formation of Geodesy

There was a great breakthrough in man's understanding of the shape of the Earth in
the seventeenth century. After Isaac Newton's formulation of the law of universal
gravitation in 1687, C. Huygens from The Netherlands, basing his findings on the
law that the gravity value on the Earth's surface increases from the equator to the
two poles, claimed in his Discours de la cause de la pesanteur in 1690 that the Earth
is an oblate spheroid flattened at the poles. In 1743, A.C. Clairaut from France
published Th ´orie de la figure de la Terre and proposed the Clairaut theorem, which
adopted the gravimetric method to determine the shape of the Earth. The research of
Huygens and Clairaut laid the theoretical foundation for study of the shape of the
Earth from a physical point of view.
In addition, W. Snell from The Netherlands initiated triangulation at the begin-
ning of the seventeenth century. This method enabled distance measurement
between two points on the Earth's surface several hundreds of kilometers or even
much farther apart, solving the problem of directly measuring the arc length on the
Earth's surface. Later, invention of the telescope, micrometer, level gauge, and